^ SIMPLE CELLS FLOATING IN THE ANIMAL FLUIDS. 27 



cavities of these cells, their walls being absorbed at the points of 

 contact, the hlood discs seem to be developed from the granules or 

 cell-germs they contain. These corpuscles are larger in the em- 

 bryo than in the adult, which fact is an argument in favour of the 

 independent circulation in the fcetus. 



According to Dr. Carpenter, the uses of the red corpuscles are 

 now definitely settled. Since they are confined nearly entirely to 

 the vertebrata, and are absent in the embryo of higher animals at 

 an early period of their development, the inference appears highly 

 probable, that they are not essential to growth or nutrition. On the 

 other hand, as they are found most abundant in those classes of 

 vertebrata which possess the highest temperature, and are known to 

 undergo important changes in the pulmonic and systemic capilla- 

 ries, — it seems highly probable that their office is, to convey oxygen 

 into the system, and carbonic acid out of it; serving, in fact, as the 

 medium for bringing the tissues into relation with the air, the influ- 

 ence of which is necessary for the maintenance of their vital activity. 



Besides the cells which have been described as floating in the 

 blood, viz., the red corpuscles, there are also found both in this fluid 

 and in the chyle and lymph, certain colourless corpuscles which are 

 observed to be present in the blood, both of the vertebrata and inver- 

 tebrata. From the latter fact it would not be wrong to infer that 

 the function of the latter must be of a general character, and imme- 

 diately connected with the nutritious properties of the circulating 

 fluid, whilst the function of the red corpuscles must be of a limited 

 character, being required only in a portion of the animal kingdom. 

 The dimensions of these corpuscles are nearly constant throughout 

 the different classes of vertebrata ; their diameter being seldom more 

 than rSOOOth of an inch ; hence it would seem improbable that the 

 one would ever be converted into the other. They have no distinct 

 nucleus, but are studded with minute granules which may occa- 

 sionally be seen in active motion within them, and which are dis- 

 charged when the corpuscles are treated with liq. potassoe. In the 

 circulating blood, they are always found on the outside of the cur- 

 rent where the motion of the fluid is slow. 



The function of these colourless corpuscles, both in the blood and 

 in the chyle and lymph, seems to be, the elaboration of plastic 

 fihrine from unorganiz able albumen. They are always found most 

 abundant where these processes are going on, in the fluids in which 

 they are contained, and their number is always in proportion to the 

 am^ount of fibrine. They are looked upon as cells of a transitional 

 character, precisely such as those developed in the germinal vesicle 

 for the elaboration of its contents. They are not in themselves des- 

 tined to form an integral part in any permanent structure, but, after 

 attaining a certain maturity, reproduce themselves and disappear, 



