THE BLOOD. 145 



Electricity causes the red blood-corpuscles to become crenated, and at length 

 mulberry-like. Finally they recover their round form and become quite pale. 



The Colorless Corpuscles. In human blood the white or color- 

 less corpuscles or leucocytes are nearly spherical masses of granular pro- 

 toplasm without cell wall. In all cases one or more nuclei exist in each 

 corpuscle. The corpuscles vary considerably in size, but average -g-^Vo- f 

 an inch (10//) in diameter. 



There was for some time a general acceptance of the original estimate 

 of Welcker that there were about 13,500 leucocytes in each cubic milli- 

 metre of normal human blood. But improved methods and appliances, 

 especially the introduction of the Thoma haematocytometer, soon proved 

 that these figures were too high, and that the number was about 7,500. 

 The latter estimate is upheld by the results of the most recent investiga- 

 tions, Rieder placing the number in adults at 7,680, Limbeck at 8, 000 to 

 9,000, and Eeinert at 5,125 at 6 A.M. and 8,262 at 4 P.M. Therefore the 

 proportion of white to red cells (counting 5,000,000 of the latter to each 

 cubic millimetre) is about 1 to 666. This proportion is in no way to be 

 regarded as a constant one in health, as considerable variations occur fre- 

 quently, even in the course of the same day. The chief physiological 

 variations are those due to the influence of digestion, of pregnancy, and 

 of infancy. 



After a full meal the white cells in a healthy adult are increased in 

 number about one-third (Rieder), the increase beginning within an hour, 

 attaining a maximum in three or four hours, and then gradually falling 

 to normal. This process is frequently modified by the character of the 

 food, the greatest increase occurring with an, exclusively meat diet, while 

 a purely vegetarian diet has usually no effect. The increase is also more 

 marked in children, and especially in infants. The essential factor is 

 probably the absorption of albuminous matter in considerable quantities- 

 this causes proliferation of leucocytes in the adenoid tissue of the 

 gastro-intestinal tract. In pregnancy there is often a moderate increase 

 in the number of white cells during the latter months. This does not 

 begin until after the third month, and is most marked and constant in 

 primiparae. After parturition the leucocytes gradually diminish under 

 normal conditions, and usually reach the normal within a fortnight. 

 The essential factor is probably the general stimulation in the maternal 

 organism. It is well established that the white cells are very numerous 

 in the new-born, though different observers have made very conflicting 

 estimates. Still all agree that there is a very rapid decrease in their num- 

 bers during the first few days, and that this is followed by a less marked 

 increase, which continues for many months. According to Rieder, who 

 is perhaps the most reliable, there are at birth from 14,200 to 27,400 

 10 



