THE BLOOD-CORPUSCLES. 157 



microscopical measurements of the corpuscles, the blood of many 

 of the mammalia can be individually detected, and distinguished 

 from that of man. The differences in the size of the corpuscles of 

 different animals are so very small, that the ordinary methods of 

 measuring these minute bodies by Weber's glass micrometer or a 

 screw micrometer, are by no means sufficient. The blood-corpuscles 

 being vesicles or cells with an extremely thin investing membrane, 

 are very much influenced by endosmotic currents, and it is clear 

 that their diameters must vary with the quantity of fluid they have 

 imbibed or given off. When the serum loses water by evaporation, 

 a current of fluid passes out from the corpuscles to the serum ; 

 their diameter must then diminish, just as on the addition of 

 water we see it increase. As in the ordinary methods of mea- 

 suring the blood-corpuscles, gradual evaporation cannot be pre- 

 vented, and the coefficient of evaporation for each special case 

 cannot be calculated, the idea suggested itself to Schmidt of 

 measuring the corpuscles of dried blood. On drying fresh blood 

 in extremely thin layers on a glass plate, the corpuscles lie with 

 their flat surfaces on the glass, adhere to it, and remain extended 

 on it after drying. Schmidt has carefully ascertained by numerous 

 measurements that the mean diameters of the blood-corpuscles in 

 this dried and extended membrane-like state, are unaffected or 

 only slightly diminished, that at least from 95 to 98$ of the 

 corpuscles of the blood of the same animal species are of equal 

 size, and finally, that the corpuscles of the blood of different 

 species of the mammalia present constant differences of size. The 

 following are, according to Schmidt, the diameters of the blood- 

 corpuscles in this state, expressed in millemetres : 



Mean. Minimum. Maximum. 



Man .... 0-0077 .... 0-0074 .... 0-0080 



Dog .... 0-0070 .... 0-0066 .... 0-0074 



Babbit.... 0-0064 .... 0-0060 .... 0-0070 



Rat .... 0-0064 .... 0-0060 .... O'OOGS 



Pig .... 0-0062 .... 0-0060 .... 0-0065 



Mouse .... 0-0061 .... 0'0058 .... 0'0065 



Ox .... 0-0058 .... 0-0054 .... 0-0062 



Cat .... 0-0056 .... 0-0053 .... 0'0060 



Horse .... 0'0057 .... 0-0053 .... 0'0060 



Sheep .... 0-0045 .... 0-0040 .... 0'0048 



These investigations constitute the first step to the diagnosis of 

 the blood of different kinds of animals. 



Colourless blood-corpuscles, or as they have been termed, 

 lymph-corpuscles, are constantly present in the blood, although 



