OBSERVATIONS ON SAPROLEGNIA INFESTING FISHES. 



167 



from the fish, were there any signs of the mature stage of the fungus. In the Achlya 

 cultures, however, this stage was reached occasionally. When the cultures of 

 Saprolegnia were about ten days old, further development being prevented by bac- 

 teria, the production of the normal zoosporangia was arrested, and what are known as 

 " resting sporangia" were formed. These were produced, in a moniliform manner, by 

 the constriction of the filaments into one or several cells in which the protoplasm 

 was not differentiated into zoospores, and which were somewhat shorter in comparison 

 to their breadth than were the usual zoosporangia. The results of most of the cul- 

 tures that were made with flies are given below : 



Tabulated results of culture experiments. 



Sources of infection. 



Aquarium water * 



Hy geia water 



Lake Michigan water 



Lagoon water • 



Central Pool water 



Fungous inoculations 



Water from experiment tank 



Water from tank containing badly diseased fish: 



Toy 



Center 



Bottom  



Bottom stirred 



Water from tank containing fish but little diseased: 



Top 



Center 



Bottom stirred 



Water from tank containing healthy fish : 



Top 



Center 



Bottom 



Bottom stirred 



Success- 

 ful. 



3 

 2 

 4 



15 

 2 



6 

 2 

 6 



3 



1 

 1 

 1 



3 

 1 



4 

 2 



Failed. 



10 

 6 



The minute structure and life-history of such fungous forms have been so thor- 

 oughly made out by eminent specialists that no investigation along this line was made, 

 save to observe those phenomena which might be easily seen with ordinary micro- 

 scopic manipulations. The fungus consists of branched, hyaline filaments, without 

 septa, except as these are found cutting off the reproductive parts of the threads. 

 It is made up of a root-like or rhizoid part that penetrates the fish, and a vegetative 

 and reproductive part that radiates from the host. The former consists of branched 

 tapering threads which pierce the tissues for a short distance, but are easily pulled 

 out. The function of this part is to obtaiu nourishment for the growth of the external 

 parts. Prostrate threads are found running through the natural slime covering the 

 fish, and from these are produced the erect radiating hyplne so plainly seen when in 

 the water. The development of these threads appears to be very rapid when viewed 

 under the microscope, although the growth made under favorable conditions in two 

 days is only about* a third of an inch. From actual measurements of filaments of the 

 fungus placed in water and watched under the microscope, it was found that certain 

 threads made a growth of about 300 microns in an hour. Two others, watched for 

 twenty minutes, gave in that time a growth of 90 and 47 microns respectively; and 

 yet another filament, observed during two periods of five minutes each, made a growth 

 of 28 microns each time. In ordinary cultures the rate of growth depends upon 

 the condition of the medium, host, etc. 



