446 BLOOD AND LYMPH. 



agglutinate quickly into masses which soon disintegrate more or 

 less completely, and it is necessary therefore in counting them to 

 mix the blood with a fixing solution which will coagulate the plates 

 and keep them from adhering together. Solutions that precipitate 

 the calcium of the blood-plasma, such as sodium oxalate, have the 

 effect of fixing the plates. The average number of plates may be 

 given as 300,000 per cubic millimeter. The extremes reported 

 vary from 200,000 or 250,000 to 778,000. Under certain patho- 

 logical conditions, especially in pernicious anemia and lymphatic 

 leucemia, their number is greatly reduced, while in the acute 

 infectious diseases there is said to be a diminution in number 

 during the period of fever, followed by a marked increase beyond 

 the normal during the period of convalescence. A number of 

 observers have stated that in hemorrhagic diseases in which there 

 is delayed coagulation and tendency to bleed there may be a great 

 reduction in the number of platelets. Duke* states that in such 

 cases transfusion of blood from a normal person removes the hemor- 

 rhagic tendency, while increasing markedly the number of plate- 

 lets. But in three days the number of platelets again falls to a 

 low level, and simultaneously there is again a tendency to spon- 

 taneous bleeding. The observation is of interest as indicating 

 that the life history of the platelets in the circulation is probably 

 very brief. 



* Duke, "Journal of the Amer. Med. Assoc.," 55, p. 1185, 1910. 



