OF SECRETION AND EXHALATION. 59 



HI. Of Transfusion of Blood.- Messrs. Prevost and Dumas found that, after bleed! ng 

 an animal until all organic actions ceased, and injecting-, within a few minutes after- 

 wards, the warm blood taken from another of the same species, until a quantity equal 

 to that taken wag restored, the animal gradually revived and took nourishment, and 

 entirely recovered, if the operation was perfectly performed. 



If, however, the blood injected was taken from an animal of a different species, pos- 

 sessing globules of the same form, but different in dimensions, the animal was very im- 

 perfectly revived, and could be rarely preserved beyond six days. The pulse became 

 in these frequent, the temperature fell remarkably, if not artificially preserved, while 

 the respiration retained its natural frequency. Immediately after the operation, the de- 

 jections became mucous and bloody; and preserved that character until death. 



If blood with circular globules, was injected into the veins of a bird, the animal ge- 

 nerally died before the operation was completed, in very violent and nervous convul- 

 sions. 



Transfusion of blood from the cow or sheep into the veins of the cat or rabbit, was 

 followed by the recovery of the animal in a number of cases. 



The blood of the sheep excited in the mallard duct the most violent and rapid con- 

 vulsions, which were immediately followed by death, as was observed to follow the in- 

 jection of the first syringcful inland-birds. (Biblioikeque Univers. Juillet, 1821.) 



Of Secretim and Exhalation. 

 Note CC. 



Opinions have been various respecting the mechanism provided for the performance 

 of exhalation and secretion. One class of physiologists contends for a separate order of 

 very minute capillaries proceeding from those carrying red blood, which they call ex- 

 halent or secretory capillaries, and devoted to these functions. Belonging to this class 

 we may reckon Haller, Hewson, Scemmering, Bichat, Chaussier, Alard, &c. As these 

 vessels cannot be demonstrated, there existence is denied by Mascagni, Prochaska, 

 Richerand, Magendie, and others, who argue, that these functions take place in the 

 sanguineous capillaries through the* medium of organic lateral pores. The fact ap- 

 pears to be that the evidence for a separate set of capillaries is equal to that for the ex- 

 istence of organic pores in the capillaries carrying red blood ; it is not easy to demon- 

 strate the presence of either; whilst both the one and the other may prove a sufficient 

 medium through which the processes will go on under the influence with which the 

 capillary vessels are endowed. The existence and efficacy of this influence is sufficiently 

 manifest, although the more minute intruments by means of which it operates, can- 

 not be satisfactorily demonstrated to our senses. 



With respect to secretion, the state of opinions and of our knowledge as to the man- 

 ner in which it takes place, or rather the mechanism provided for its performance, is 

 similar to what we have shown to exist on the subject of absorption and on that of the, 

 minute capillaries. In stating the opinions on these subjects, and those lately espoused 

 by M. Alard. we gave the views of those who contend for the existence of minute 

 lymphatics running into the venous capillaries, in a similar manner to that in which ex- 

 halent vessels are supposed, as stated above, to proceed from the arterial capillaries. 

 But the latter set of vessels has been as little seen as the former. This, however, in a 

 matter of this nature, is not a sufficient proof against their existence. Other physiolo- 

 gists, on the other hand, contend that exhalation and secretion take place through 

 means of pores analogous to those which are supposed to be instrumental in the phe- 

 nomena of absorption ; and that the process is entirely one of transudation. But the 

 same objection may be offered against the existence of pores as to that of the exhalents 

 or secreting capillaries in -question. 



We believe that the precise way in which exhalation and secretion take place can- 

 not be readily demonstrated to the senses, that the one apparatus may explain the 

 process as well as the other, that secretion as well as absorption, are not mechanical 

 processes, although there are apparatuses, or subordinate instruments, provided for 

 their performance, and that they are essentially vital operations, and under the control 

 of the vital influence with which the capillaries themselves, and the organs to which 

 they belong, are endowed. 



As to the question of pores, it must be granted that the solids of the body, and the 



