PROPERTIES OF THE BLOOD. 437 



throughout the whole animal scale ; whilst the presence of red corpuscles in 

 that fluid is limited to the vertebrated classes. Hence it would not be wrong 

 to infer, that the function of the colourless corpuscles must be of a general 

 character, and intimately connected with the nutritious properties of the circu- 

 lating- fluid ; whilst the function of the red corpuscles must be of a limited 

 character, being only required in one division of the animal kingdom. Fur- 

 ther, it has been noticed by Mr. Gulliver, that in the very young embryo of 

 the Mammalia, the white globules are nearly as numerous as the red particles : 

 this, Mr. Gulliver has frequently noticed in foetal deer of about 1 inches long. 

 In a still smaller foetus, the blood was pale from the preponderance of the white 

 corpuscles. It is, therefore, a fact of much interest that, even in the Mam- 

 miferous embryo, at the period when growth is most rapid, the circulating 

 fluid has a strong analogy to that of the Invertebrata. It then, too, bears in 

 other respects the most striking analogy to chyle ; since it consists of the fluid 

 elaborated from the organizable matter supplied by the parent, and directly 

 introduced into the current of the circulation. The function of the placental 

 vessels may be regarded as double : for they are at the same time the channel 

 through which the alimentary materials supplied by the parent are introduced 

 into the circulating system of the foetus, and the medium of aerating the fluid 

 which has traversed the foetal system. Hence the placenta may be regarded 

 as at once the digestive and the respiratory apparatus of the foetus ; and the 

 fluid circulating through the cord, as at once chyle and blood. It is not until 

 the pulmonary and lacteal vessels of the embryo have commenced their inde- 

 pendent operation, that the distinction between the blood and the chyle of the 

 foetus becomes evident ; and we should expect, therefore, to find that the circu- 

 lating fluid, up to the time of birth, contains a large proportion of white cor- 

 puscles, which is actually the case. There is a gradual decrease, however, 

 in their proportional number, from the earlier to the later stages of embryonic 

 life, in accordance with the diminishing energy of the formative processes. 

 It has been also observed by Wagner,* that the number of colourless corpuscles 

 is always remarkably great in the blood of well-fed frogs just caught in the 

 summer season ; and that it is very small in those that had been kept long 

 without food, and in those examined during the winter. The most remarka- 

 ble evidence, however, of the connection between the generation of white cor- 

 puscles in the blood and the production of fibrin, is derived from the pheno- 

 mena of Inflammation. A decided increase in the normal proportion of fibrin 

 in the blood (from 2 to 3 parts in 1000), may probably be looked upon as 

 the essential indication of the existence of the inflammatory condition ( 591 a}. 

 That this production of fibrin is due to a local change can scarcely be doubted, 

 since it is frequently observed to commence before any constitutional symp- 

 toms manifest themselves ; and it may be regarded, in fact, as one cause of 

 these symptoms. Now the recent microscopic observations of Mr. Addisont 

 and Dr. Williams,;}; which were made independently of each other, have 

 established the important fact, that a great accumulation of white corpuscles 

 takes place in the vessels of an inflamed part: this seems to be caused at first 

 by a determination of those already existing in the circulating fluid towards 

 the affected spot ; but partly by an actual increase or generation of these bodies, 

 which appear to have the power of very rapidly multiplying themselves. 

 The accumulation of white corpuscles may be easily seen, by applying irri- 

 tants to the web of a frog's foot. Mr. Addison has noticed it, in the human 



* Op. cit. p. 245. 



f Medical Gazette, Dec., 1840; Jan. and March, 1841. 



t Medical Gazette, July, 1841; and Principles of Medicine, [Amer. ed. by Dr. Clymer, 

 pp. 214, 215.] 



