MILNEK FISHEKIES OP^ IHE GREAT LAKES. 31 



foraia sbipmeut, was crowded down with a piece of board, aud may 

 have, in consequence, rendered the package more completely air-tight 

 than in the shipments referred to similarly packed. 



A later shipment arrived in most excellent condition. The cups in 

 the cases were made four by four inches square, by two deep, with no 

 packing between the cans, and the eggs packed in moss. The most 

 ample ventilation was i^rovided for in the egg-cases. 



The oxygen given off by live moss is probably the principal reason 

 for its special adaptation in packing eggs for shipment. 



Dr. Hansom's experiments on the effect of heat have also a practical 

 value in the treatment of hsh-ova, both in transportation and in the 

 troughs. He says : "Some eggs in the stage of active contraction were 

 cooled until the thermometer placed on the cell stood at 32'^ F. They 

 all became still, and their yelks globular. They were not frozen ; and I 

 do not doubt that their temperature was higher than that indicated by 

 the thermometer." The contractions were afterwards restored by a 

 weak galvanic current. In another observation "I froze the water in 

 which the eggs were placed, so that some of them were completely, and 

 others incompletely, frozen. The frozen eggs were all more or less 

 opaque, and had their inner sacs ruptured, and emptied of yelk in va- 

 rious degrees, aud their formative yelks lobulated, and darkly granu- 

 lar. Those which were least frozen were slightlj^ opalescent only, and 

 when allowed to thaw they contracted as before, ultimately going 

 on to cleave in an irregular manner, the ruptures in their sacs having 

 healed. Slighter reductions of temperatures to 40° and 48° F., retarded 

 without destroying the contractions. In such cases the commence- 

 ment of cleavage was delayed. By raising the temperature moderately 

 the movements were accelerated ; but at about 80^ F. (it is difficult to 

 speak with certainty of the temperature actually obtained by the ob. 

 ject) the contractions were arrested; the yelk-ball becoming globular, 

 and the oil-globules being scattered. Such eggs, however, soon recov- 

 ered themselves when left at 58° F., and cleft in even less time than eggs 

 did which had not been warmed. In other eggs, heated in a cham- 

 ber at 102° F., the cleavage was retarded to three times the usual 

 period, and when it took place was wanting in symmetry. The yelk 

 began to become opalescent at about 103° F. ; but a true coagulation of 

 the albumen did not take place, the yelk being fluid, and opaque. Thus 

 a temperature too low or too much elevated retards or arrests the 

 contractions, but they are not destroyed before commencing physical 

 and chemical changes set in." 



Whether the point at which the contractions of the yelk ceased was 

 the point at which vitality left the egg, might or might not have been 

 the fact, but it is quite evident that the egg was, at the temperatures 

 stated, in an abnormal state, aud the necessity of sustaining a tempera- 

 ture around the eggs of fishes between these extremes is nppnrent, if 

 they are to be kept in their most favorable condition. 



