140 



Part III. — Sixteenth Annual Report 



C. — Volume of the Ova. 



This was obtained either by calculation from the diameter or by 

 estimating the volume of the water displaced by a known number of 

 ova. I have omitted giving the volumes of the ova, as they are fully 

 given in Dr. Fulton's paper. 



D. — Weight of the Ova. 



This had to be done very carefully. The ova were freed from adherent 

 tissue or fluid, numbered, placed between weighed watch-glasses with 

 clip to lock them together, and then weighed in Sartorius balance. This 

 was done as quickly as possible, so that drying of the ova might be 

 avoided. A better method, and one which I employed also, was to weigh 

 out two portions of ova, put one set into alcohol, and after the ova had 

 lain for some time in the alcohol they were numbered. Knowing the 

 weight before putting into alcohol, and now knowing the number, you 

 knew the weight of each fresh. In this way you knew the weight and 

 number of the ova in the other portion which can be weighed and dried. 



E. — Percentage of Water in the Ova. 



The ova, after being weighed as described under D., were placed in a 

 drying oven, and kept first of all at temperatures varying from 80° to 90* C; 

 then the temperature was gradually raised until it reached finally 105° to 

 110°. They were kept at this temperature until of constant weight. 

 The loss of weight gave the amount of water in each ovum, and, of course, 

 the percentage was easily calculated. 



F. — Percentage Composition of the Ova. 



Of the solids of the ovum after driving off the water, the most impor- 

 tant are the nitrogen and phosphorus holding bodies, the fat and salts. 

 It would require much more time than I had at my disposal to make a 

 complete analysis of all the ova sent me, so that in many cases I had to 

 limit myself to the nitrogen and phosphorus. From the amount of 

 nitrogen we can roughly calculate the probable amount of albumen, if 

 such bodies as lecithin and nitrogen-holding salts can be excluded. 



The nitrogen was estimated by the well-known Kjeldahl method, all 

 the nitrogen-holding substances having their nitrogen transformed into 

 (N 114)2 ^^Ai from this the ammonia distilled off and estimated. 



The phosphorus was estimated by Kjeldahl-Weibull method — that is, 

 incineration of the ova with On SO4, Kg SO4, and So^ ; and the 

 phosphate found estimated by the Ammonium-Molybdate method, the P. 

 being weighed as magnesium-pyrophosphate, and phosphorus reckoned 

 from it. 



Fat loas estimated by extracting the dried and weighed ova by ether in 

 Soxhlet's apparatus until no more weight was lost, and then the ova were 

 finally extracted for some hours with boiling alcohol. 



The loss in weight which the ova underwent gave one the amount of 

 fat and lecithin present, or the amount of residue obtained after removal 

 of the ether and alcohol by distillation gave the fat and lecithin present. 

 Having estimated the amount of lecithin (in the way I shall next 

 describe), you get the amount of fat by subtracting the amount of the 

 former from the combined weight. 



