THE BLOOD. 241 



form and composition of the corpuscles are maintained under normal 

 physiologic conditions. This fluid, therefore, is preservative of the 

 structure and function of the corpuscle. When examined micro- 

 scopically with a view of determining their histologic features, the 

 plasma must be diluted, and in consequence they rapidly undergo 

 physical and chemic changes from the absorption or loss of water. 

 To prevent these effects the corpuscles must be immersed in a fluid 

 containing a percentage of salts approximating that of the plasma. 

 Under such circumstances they will neither absorb nor give up 

 water. Such a fluid is found in the physiologic salt solution, which 

 contains 0.64 per cent* sodium chloric!. Tms fluid maintains the 

 chemic equili brium oi ike corpuscTesiand is therefore said to be 

 isotonic to the corpuscle. 



~~TT~HIstilled water be added to the drop of blood, the corpuscle 

 absorbs it, swells up, and assumes a more or less spherical form, 

 sometimes cup-shaped. The hemoglobin dissolves out and the 

 stroma becomes almost invisible. Its presence can be detected by 

 the addition of iodin. The addition of salt solutions, e. g., sodium 

 chlorid, sodium sulphate, ammonium chlorid, etc., which increase 

 the density of the plasma, cause a shrinkage of the corpuscles so that 

 they assume a crenated or notched appearance. Dilute solutions of 

 acetic acid, of alkalies, especially potassium and sodium hydrate, 

 cause the corpuscles to swell, to lose their color, dissolve, and en- 

 tirely disappear. Many other agencies of a physical and chemic 

 nature, such as heat 60 C., electricity, bile salts, the vapor of 

 chloroform, ether, ammonium sulphocyanid, etc., also destroy the 

 integrity of the corpuscles, and cause the hemoglobin to separate 

 from the stroma and diffuse into the plasma without itself under- 

 going any appreciable change in composition. The blood at the same 

 time will become transparent and change to a dark red color, to 

 which the term "lake color" has been given. 



The Corpuscles of Other Vertebrated Animals. In all mam- 

 mals, with the exception of the camel, llama, and dromedary, the 

 red corpuscles present the same shape and structure as the corpuscles 

 of man, and may be described as circular, flattened, biconcave disks. 

 In the animals excepted the corpuscles are oval. The size, however, 

 varies in different animals from 0.0092 mm. (^rW i ncn ) m the ele- 

 phant to 0.0023 mm - (TTOT i ncn ) m tne musk-deer, while in most 

 animals the average lies between 0.0084 mm. and 0.0050 mm. Inas- 

 much as the question may arise as to whether the corpuscles of any 

 given specimen of blood are those of a human being or of some other 

 mammal, a knowledge of the size of the corpuscles becomes a matter 

 of medicolegal as well as of physiologic interest. Though the 

 differences in size are slight, yet it is possible for skilled microscopists, 

 when examining fresh blood, to make a diagnosis between the cor- 



16 



