540 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in the same way as it attacks the dead insect, and that it is the sole 

 cause of the disease, whatever circumstances may, in a secondary 

 manner, assist its operations. 



2. That death may result without any other organ than the skin 

 being attacked, and that, under these circumstances, it is the conse- 

 quence partly of the exhaustion of nervous energy by the incessant 

 irritation of the felted mycelium with its charge of fine sand, and 

 partly of the drain of nutriment directly and indirectly caused by the 

 fungus. 



3. That the penetration of the hyphse of the Sajprolegnia into the 

 derma renders it at least possible that the disease may break out in a 

 fresh-run salmon without re-infection. 



4. That the cause of the disease, the Saprolegnia, may flourish in 

 any fresh water, in the absence of salmon, as a saprophyte upon dead 

 insects and other animals. 



5. That the chances of infection for a healthy fish entering a 

 river are prodigiously increased by the existence of diseased fish in 

 that river, inasmuch as the bulk of Saprolegnia on a few diseased fish 

 vastly exceeds that which would exist without them. 



6. That as in the case of the potato disease, the careful extirpation 

 of every diseased individual is the treatment theoretically indicated, 

 though, in practice, it may not be worth while to adopt that treat- 

 ment. 



Formation of Saccharomyces in Nutrient Fluids containing 

 various Proportions of Nitrogen.* — M. Hayduck finds asparagin 

 especially well adapted as a source of nitrogen for Saccharomyces. 

 The mineral ingredients of the nutrient fluid were a mixture of 

 50 g. acid potassium phosphate, PH 2 K0 4 and 17 g. crystallized 

 magnesium sulphate ; and the following results were obtained : — 



1. The nitrogen contained in a nutrient fluid is assimilated by 

 the yeast only up to a certain degree of concentration ; and above this 

 limit the nitrogen is not used in the production of yeast. (2) In all 

 the experiments an excretion of nitrogen was observed. (3) When 

 formed in very dilute solutions the yeast contains a constant minimum 

 proportion of nitrogen ; as the proportion of nitrogen in the solution 

 increases, the amount of yeast formed remains the same, while the 

 proportion of nitrogen in it increases. But beyond a certain limit, 

 the amount of nitrogen in the fluid increases neither the amount of 

 yeast produced nor the proportion of nitrogen in it. (4) The fer- 

 menting power of the yeast depends partly on the proportion of nitrogen 

 contained in it. (5) Yeast containing a large amount of nitrogen 

 can increase in a pure solution of sugar, a portion of the nitrogenous 

 contents of the mother-cells being used in the formation of the 

 daughter-cells. (6) The growth of the yeast may be affected by the 

 formation of one or more products of fermentation, alcohol especially 

 exerting a prejudicial influence upon it. 



* Zeitschr. f. Spiritusindustrie, 1881, p. 173. See Bot. Centralbl., x. (1882) 

 p. 153. 



