In a similar manner the study of the alterations which the fousel oil of the potato undergoes by the action of oxygen, led to the discovery of the existence of a definite relation between this compound and valerianic acid; and the numerical formulæ of these two compounds showed that they stand in the same relation to one another as the common spirit of wine stands to acetic acid.

Chemical relation between Urea, Uric Acid, Allantoin, and Oxalic Acid. The urine of man contains urea, and, in many instances, likewise uric acid. This acid is not found in the urine of certain classes of animals, whilst the urine of other classes, again, contains no urea. The quantity of urea in urine decreases in proportion as that of the uric acid increases. The urine of the fœtus of the cow contains allantoin. Oxalic acid forms almost constantly a constituent of the urine of man. Changes in certain vital processes in the organism are accompanied by corresponding changes in the nature, quantity, and condition of the compounds which are secreted by the kidneys. It is the task of the chemist to express quantitatively, by numerical formulæ, the relation in which these various substances are observed to stand to one another, and to the processes occurring in the organism.

How Chemistry proceeds to express these relations.

Chemistry, in the first place, substitutes for the terms urea, uric acid, allantoin, oxalic acid, &c., numerical formulæ expressive of the respective quantitative composition of these compounds: these formulæ, however, do not yet establish any mutual relation between these several substances; but my investigating the deportment and properties of these compounds, and the alterations which they undergo under the influence of oxygen and of water,-consequently, of those substances which perform a part in their formation or alteration within the organism,-chemistry arrives finally at terms which establish a definite and unmistakeable connexion and mutual relation between these four compounds. Upon addition of oxygen, uric acid separates into three products -viz., allantoin, urea, and oxalic acid. A larger supply of oxygen converts uric acid into urea and carbonic acid; allantoin presents the composition of urate of urea. The comparison of the conditions under which uric acid is found, in chemical experiments, to change into urea with those that attend this process in the organism, leads to the conclusion, either that these conditions (in the case before us, supply of oxygen) are the same in both cases, or that they differ from each other. These differences furnish new startling points for further investigation, which finally leads to the elucidation of the process in the organism.

Urea and uric acid are products of the alterations which the nitrogenous constituents of the blood undergo under the influence of water and of oxygen.The nitrogenous constituents of the blocd are identical in composition with the nitrogenous constituents of the food. The relations between the latter and uric acid,-between urea, and the oxygen of the air, and the elements of water,the quantitative condition of the formation of urea, &c., chemistry expresses in formulæ, and explains and elucidates them thereby as far as its own province extends.

Functions of the Chemical Formula.

It must be evident, even to those not conversant with chemistry, that the difference in the respective properties of two bodies containing the same elements, is dependent either upon a different mode of arrangement of the elements of which they respectively consist, or upon a quantitative difference in the respective compositions of the two bodies. Now, the formulæ of the chemist are intended to express this difference in the mode of molecular arrangements, or the quantitative differences which accompany the qualitative ones. Chemistry at present is unable, notwithstanding the most careful analysis, to establish with positive certainty the composition of an organic body, so long as the quantita

tive relation remains undetermined, in which this body stands to another substance, of which the formula has been clearly and positively established.

It was in this way alone that chemistry succeeded in establishing the formulæ of fousel oil, and oil of bitter almonds, for instance; and in cases where direct observation fails to discover relations of mutual dependence, the chemist is obliged to create such relations by his art. For this purpose, he endeavours to resolve the body under examination into two or several products: he examines the products, which he thus derives by the action of oxygen, or of chlorine, of alkalies and acids, upon the substance of which he is desirous to fix the formula; and it is by these means that he succeeds finally in obtaining one or several products, of which the composition, and consequently the formulæ, are clearly and distinctly known. From the formula of these products he finally deduces the formula which he is in quest of, and derives thus his knowledge of the whole from that of one, several, or all the parts constituting that whole.Thus, for instance, analysis leave us altogether in the dark regarding the number of equivalents of carbon, hydrogen, and oxygen that constitute the sugar atom; the skill of the chemist fails to furnish him with a positive proof, demonstrative of the correctness of his analysis of salicin, or of amygdaline; but sugar combines with oxide of lead, and is, by fermentation, resolved into carbonic acid and alcohol, into two compounds, consequently, of which the formulæ are perfectly and distinctly known; amygdaline is resolved into hydrocyanic acid, oil of bitter almonds, and sugar: salicin into sugar and saligenine..

Use and Import of Chemical Formulæ.

It is clearly evident, that from the known weight of a substance, and the known weights and formulæ of one or two, or all of the products derived from it, the number and the relative proportions of one or two, or all of its elements, in other words, its own formula, may be deduced, and thus the results of the analysis may be verified or corrected.

Reason why the Chemist studies the Products resulting from the Decomposition of Bodies.

The preceding passages show clearly what is the real use and import of chemical formula. The correct formula of a substance expresses the quantitative relations in which that substance stands to one, two, or several other bodies. The formula of sugar expresses the sum total of the elements of sugar, which combine with an equivalent of oxide of lead, or the quantity of carbonic acid and of alcohol into which sugar is resolved upon fermentation. It will be readily understood now why the chemist should be so frequently obliged to resolve into numerous products the substance of which he is desirous to fix the composition, and why he should be obliged to study the various compounds which the substance under examination forms with other bodies. Every one of the results arrived at by such investigations and experiments of the chemist serves as a control for the correctness of his analysis. No formula, deserves implicit confidence, unless the body, the composition of which it is intended to express, has been subjected to these operations.

Misapplication of Formula to purposes for which they are not intended. Some modern physiologists, forgetting that the knowledge of the relations existing between two phenomena ought to precede the numerican expressions, have turned the formulæ of the chemist into a sort of unmeaning play of numbers; instead of applying them to their legitimate purpose-viz., to express actually existing relations of mutual dependence between two phenomena, &c.,these physiologists would endeavour to establish, by these means, relations which do not exist in nature, or, at all events, have never been observed to exist.*

* Thus VALENTIN says, at page 174, vol, i., of his "Manual of Physiology;"— "Microscopical anatomy shows that there exists in the brain and spinal marrow a

Hopes.

But the time will come, although the present generation will hardly live to see it, when numerical terms in chemical formulæ shall have been determined for all the normal functions, processes, and forms of the organism; when the variations and deviations in the functions of every individual part of the organism shall be measured by corresponding variations in the composition of the matter of which these parts respectively consist, or of the products derived from this matter; when the effects produced by morbific causes, or by remedies, should be quantitatively determined; and when a better and more rational method than obtains at present in physiology shall lead to the knowledge of all the conditions of the vital phenomena, and introduce perspicuity and precision into the explanations and elucidations of these phenomena. Posterity will then hardly believe that there was a time when the share that chemistry is intended to take in these acquisitions was contested, when men of science could remain doubtful and uncertain regarding the mode in which chemistry might assist them in the investigation and comprehension of vital phenomena.

2.-Generation and Development.

Ovum of Mammalia, and the several changes which it undergoes.-Bischoff has recently published a new work containing the results of his researches on the development of the ovum in the bitch.* The chief conclusions at which he has arrived may, on account of their relation to the development of the inammiferous ovum generally, be briefly stated here. Much of the matter which they contain, however, has been already made known by the author in his previous works, as well as by the researches of others, and may be found fully discussed in the elaborate report on the "Ovum of Man and the Mammifera," by Mr. Wharton Jones. 1. The unimpregnated ovum of the bitch whilst in the ovary, consists, like that of all mammalia, and indeed of all other animals, of a vitellary membrane, termed zona pellucida,t of a vitellus or yelk, of a germinal vesicle, and a germinal spot. The average size of the ovum is 1-15 of a line; that of

mixture of grey and white substances, and that albumen and oil are associated together in these organs. Instead of acting upon this knowledge of the anatomist, the chemists analyzed this mixture in unknown proportions of albumen and fat, as consisting wholly of fat; this analysis led them to the discovery of a peculiar nitrogenous, fatty acid, upon which they bestowed the name of Cerebric acid,' endeavouring, at the same time, to support, upon theoretical grounds, the anomaly of the existence of a nitrogenous fat. But by a chemical deduction, based upon MULDER'S formula of protein, it may be demonstrated, that the analyzed substance consists simply of what the results of the anatomical and microscopical researches would lead us to expect-viz., of a mixture of albumen, fat, and phosphorous.

Thus, this apparent anomaly which the cerebral substance would seem to offer, according to the chemical analysis, has, in reality, no existence.

* Entwicklungsgeschichte des Hunde-Eies, 1845.

+ Brit. and For. Med. Rev.. vol. xvi., 1843.

In regard to the structure of the zona pellucida surrounding the unimpregnated ovum, Bischoff still agrees with Mr. Wharton Jones in considering it to be formed of a homogeneous transparent membrane, without vessels, fibres, or cells, and to correspond in all respects to the vitellary membrane of the bird's egg. The thickness, firmness, and elasticity of this membrane, as well as the fact that the ova of no other class of animals in their primary state are provided with albumen, are all opposed to the truth of the theory held by Krause and others, that this zona pellucida is composed of albumen, either alone or enclosed in a membrane. Neither is there any proof of the existence of any other membrane within this zone which could correspond to the proper vitellary membrane, and the probability is, that as Coste (last Report, p. 296) and others believe, the granules composing the vitellus are held together either simply by their own cohesive force, or by the help of some clear viscid substance.

the germinal vesicle 1-60, and that of the germinal spot 1-240 of a line. Within the ovary, the ovum is imbedded in a layer of cells which, in the form of a membrane (membrana granulosa,) lines the internal surface of the Graafian follicle. At the point of this membrane where the ovum is situated, the cells are accumulated in larger quantity than elsewhere, and adhere to the vitellary membrane of the ovum, constituting the so-called discus proligerus. 2. The ova in the bitch (as probably in most other mammalia) arrive at their maturity in the ovary at certain periodic times, corresponding with the periods of heat in the same animal. As circumstances denoting the occurrence of this state of full maturity of an ovum, may be regarded-the swollen state of the Graafian follicle, the larger size and fuller appearance of the ovum itself, the elongation of the cells of the discus proligerus into the state of fine fibres, and lastly, the disappearance of the germinal vesicle. The latter event indeed sometimes does not occur until the ovum has escaped into the Fallopian tube. With regard to the germinal spot at this time, nothing certain can be said. 3. When an ovum is fully matured, it escapes from the ovary, and passes into the Fallopian tube, whether sexual intercourse has taken place or not. If copulation does not now occur, or if access of the seminal fluid to the ovum is entirely prevented, the ovum dies. Inasmuch, however, as the sexual desire is especially strong at this period, copulation and consequent impregnation are usually effected. Even if the ovum has not left the ovary at the time of coition, it may still be impregnated by the seminal fluid passing up the Fallopian tube to the ovary; or it may, at a later period, meet this fluid on its way. There is plenty of time for this to happen, for after leaving the ovary the ovum is usually from six to eight days in passing along the Fallopian tube to the uterus, during any part of which period it may be impregnated on coming into contact with the seminal fluid. When once arrived at the uterus, however, it is no longer capable of being fecundated, and by the time it has advanced to within a few lines of this its destination, the bitch will no longer allow itself to be lined. 4. The number of ova which at a single period of heat escapes from the ovary varies somewhat. They almost all escape at about the same time, there never being an interval of a day between the departure of any two; they are all therefore found accumulated together at the same part of the Fallopian tube, and present nearly the same degree of development. The several Graafian follicles which are distended at the time of heat do not all discharge their ova; some retain their ova, which eventually break up and disappear. 5. Previous to the discharge of the ovum from the fully matured Graafian follicle, there begins to grow from the internal surface of this follicle a peculiar substance, under the form of granulations; and after the follicle has burst, and the ovum escaped, this new growth becomes further developed, so as to form a true corpus luteum. The presence of such a new structure in the ovary must therefore always be regarded as a certain proof of a Graafian follicle having burst, and of its contained ovum or ova (for in some cases a single follicle contains two, or possibly even more ova within it) having escaped; though not as a proof of coition and consequent impregnation having been effected. [This account, as was stated in the first Report,* must be modified in its application to the corpus luteum in the human ovary, in which this new growth in its perfect form probably never occurs, except as a consequence of conception.] 6. In order that fecundation of an ovum may take place, the seminal fluid must come into actual contact with it. After copulation, spermatozoa in a state of active movement may be sometimes found in abundance on the ovary; but whether or not, they are always present in the Fallopian tubes, and consequently around the ova, if these have already arrived there. It has never been clearly shown, neither is it probable, that a sperma

* Half Yearly Abstract, vol. i., p. 277.

tozoon enters bodily into an ovum.* The action of the semen on the ovum is probably a chemical one; and it appears tolerably certain that (as suggested by Valentin) the fluid part of the seminal secretion is the material by which fecundation is effected, and that the office of the spermatozoa is two-fold: first, by their energetic movements to act as carriers of the seminal fluid to its destination at the ovum; and secondly, by the same active movements, to maintain in its integrity the due mixture and composition of the liquor seminis. The spermatozoa therefore probably acts towards the liquor seminis a part somewhat similar to that performed by the corpuscles of the blood towards the liquor sanguinis. So soon as the spermatozoa lose their movements or are separated from the seminal fluid, the fecundating power of the latter is lost. The liquor seminis, or its fecundating part, most probably enters the ovum by imbibition through the zona pellucida. 7. During the passage of the ovum along the Fallopian tube, the cells of the discus proligerus, which have hitherto surrounded the zona pellucida, gradually and entirely disappear, so that eventually the latter is left quite bare; no deposit of albumen on it takes place, such as is observed to be the case in the rabbit's ovum (as discovered by Mr. Wharton Jones.)— The ovum itself, as it passes along the Fallopian tube, becomes only somewhat larger in size. 8. When arrived towards the lower extremity of the tube, the first certain signs of the development of the ovum take place. These consist in a division of the yelk into smaller and smaller globular masses, which division takes place in geometrical progression with the factor two. These globules into which the entire mass of the yelk is eventually broken up are not cells, but simply agglomerated heaps of the yelk-granules unsurrounded by a membrane, and containing each in its centre a clear unnucleated vesicle, very similar to a fat-vesicle. The cause of this progressive division of the yelk and the source of the clear vesicle in the centre of each ultimate globule are points still in obscurity. It is probable, however, that the central vesicle is the cause of this division and subdivision, and that this vesicle itself is derived from the germinal vesicle or its nucleus.f 9. The forces concerned in propelling the seminal fluid along the genital passages towards the ovum are probably threefold, and consist, first, of the impetus furnished by ejaculation, which carries the semen quite into the uterus; secondly, of a contractile movement of the uterus and Fallopian tubes, which commences at the vagina, and thence proceeds onwards towards the ovaries : and thirdly, of the energetic movements of the spermatozoa themselves. The ciliated processes of the epithelium lining the uterus and Fallopian tubes can have no share in producing this onward movement of the seminal fluid, since their vibrations take place in a direction contrary to that along which the seminal fluid is advancing. 10. The forces concerned in conveying the ovum from the ovary along the Fallopian tube to the uterus are probably derived partly from the movements of the vibratile cilia situated along the Fallopian tube, and partly from the contraction of the Fallopian tube itself. 11. When first arrived in the uterus the ovum has much the same appearance which it presented when in the Fallopian tube, and the division of the vitellus still continues. Shortly, however, the small globular masses into which the vitellus has divided are developed into cells; a delicate membrane forming around each mass, and the clear vesicle in its centre consti

* In the present, as in his previous works, Bischoff states (p. 17,) that although he has repeatedly and carefully searched for spermatozoa in the interior of ova taken from the bitch as well as from the rabbit, he has never succeeded in finding them, and that he has been equally unsuccessful in his attempts to find the opening or fissures in the zona pellucida through which the spermatozoa might be enabled to enter the ovum, as described by Mr. Martin Barry.

+ For Coste's account of the Metamorphoses of the Vitellus, which corresponds closely with the above, see last Report, p. 256.

+ This movement has been hitherto observed only in bitches and rabbits. There is no proof of its existence in the case of the human female.