196 H. S. H. WARDLAW. 



From this table it will be seen that the average density 

 is highest at the second pregnancy, and falls as the number 

 of pregnancies increases; the average percentage of total 

 solids is slightly lower at the first pregnancy than at the 

 subsequent; the average percentage of fat rises till the 

 third pregnancy, and then begins to fall; the average per- 

 centage of solids not fat is higher at the first than at sub- 

 sequent pregnancies, although there is a rise after the 

 third; the average percentage of protein, like that of the 

 fat rises, until the third pregnancy and then falls; while 

 the average percentage of solids not fat and not protein, 

 falls after the first pregnancy, but increases again after 

 the third. 



9. Effect of volume of sample and of period of rest on 

 fat-content of human milk. 



With regard to the effect of the volume of a sample of 

 human milk obtained from the breast one might expect 

 from the work of Engel and others quoted in this connec- 

 tion that, in general, the smaller the volume of a sample 

 was the higher the percentage of fat in it would be. In 

 the present case, when the volume of the sample was 

 between 15 cc. and 24 cc. the average percentage of fat 

 was 2*66; and when the volume of the sample was between 

 25 cc. and 35 cc. the percentage of fat in it was 3*09. These 

 figures are more in accord with the statement of Helbich 

 (loc. cit.) than with that of Engel, and show no very evident 

 reciprocal relation between the volume of the sample and 

 the percentage of fat in the milk. 



The effect of the time of rest since the last withdrawal 

 of milk from the mammary gland on the percentage of fat 

 in the milk yielded should be similar, according to the 

 workers cited above, to that of the volume of the sample, 

 that is, the relation should be an inverse one. When 

 samples of milk of approximately equal volume, but obtained 



