3i8 Natural History Bulletin. 



through, sometimes becoming stuck for some seconds. Rolls 

 of coloured corpuscles. would float up to this strait, detach 

 themselves one by one, squeeze through the narrow way, and 

 go floating away in the plasma stream. Soon some obstruc- 

 tion would check the journey of these coloured corpuscles, 

 and as soon as they approached one another, rouleaux were 

 formed, in many instances the corpuscles taking the same 

 relative position that they occupied before entering the nar- 

 now strait. 



Leucocytes. 



Size. — One hundred leucocytes were measured. The aver- 

 age size was ^i%^ of an inch, or about 1 1//. 



The largest were ^isv of an inch, or about i8/<. Three of 

 these were found. 



The smallest were »oVir of an inch, or about 5,^. Two of 

 these were found. 



Number. — An enumeration of leucocytes was made March 

 4th, at the same time that the coloured corpuscles were 

 enumerated. The leucocytes in fifty squares were counted, 

 and the estimate of 294,800 leucocytes per cubic millimeter 

 was made. Another enumeration was made March 7th, at 

 the time of the enumeration of coloured corpuscles. At this 

 time the leucoc3'tes in one hundred squares were counted, 

 and the result was 340,000 leucocytes per cubic millimeter. 

 These estimates give the proportion of leucocytes to coloured 

 corpuscles as i to 13. The writer's first glance through the 

 microscope at this blood, led him to exclaim that the leuco- 

 cytes were as numerous as the coloured corpuscles. Prof. 

 Calvin's first observation led him to make the same exclama- 

 tion, and Mr. Houser also entertained the same idea. As 

 shown by the hasmacytometer, the proportion of leucocytes 

 to coloured corpuscles was as i to 13. The illusion was due 

 to two facts. First, we are accustomed to see but a few leuco- 

 cytes in any one field; and second, the coloured corpuscles 

 were in rouleaux, and only the edge of each was seen. 



