363 
Physiology of the Saprolegniaceae. 
species in great detail. He found it grew very luxuriantly on the various 
substances which Maurizio had used, and evidently had no trouble in 
keeping it sterile, once he had isolated the gemma. 
Davis (’ 04 ) does not give any details as to how he isolated his material. 
He does not seem to insist on its having been entirely sterile at all 
times. 
My own method was gradually developed from the hints thrown out 
by preceding investigators, and although far from meeting all the require- 
ments of the whole family, it has made it possible to isolate the species of 
the genus Saprolegnia from both bacteria and other species and genera of 
the water moulds with great ease and certainty. 
The fungi were obtained, as is usual, from water brought in from as 
many habitats as possible — river, ponds, lakes, ditches, brooks, and springs 
—and contained algae or other aquatic plants or merely decaying vegetable 
matter. The separate collections were placed in jars in the laboratory 
which were then filled up with distilled water. The tap water is well 
known to be deleterious to many algae, and they do much better in their 
native water or in distilled water. The jars were all labelled, and into each 
was thrown a fly or a small piece of dry beef ; the former is better, as 
bacteria attack the beef too quickly. After being exposed twenty-four 
hours this bait was usually found to be inoculated, especially if the jars, 
which were kept in a cool window, had been warmed up somewhat by the 
sunshine. It is well to expose the bait as short a time as possible. The 
fly or meat was then transferred to sterile glass capsules containing distilled 
water, and in a few days was covered by the characteristic zone of the 
fungus. To remove the bacteria, a piece of the mycelium was cut off with 
scissors and transferred to a Petrie dish containing beef-gelatine. 
As satisfactory results are only obtained from the right sort of beef- 
gelatine, the method of preparation may be given at this place. About 
half a kilogram of fresh lean beef is chopped fine and placed in a glass jar 
and one liter of distilled water poured over it. After standing twenty-four 
to thirty-six hours in a cool place the water is siphoned off and to every 
500 cc. is added 52 to 55 grams of sheet-gelatine. The mixture is then 
heated on the water bath and stirred till all the gelatine is dissolved. After 
allowing it to cool to between 45 0 and 50° C., white of egg is added and 
the mixture thoroughly shaken to a froth, when it is placed in a steam 
sterilizer and boiled thirty minutes. It is then filtered through several 
layers of filter paper into Erlenmeyer flasks as stock material. The 
gelatine should be perfectly clear and become hard when set out into the 
ordinary room temperature. Sterilization is repeated on the two following 
days. From the stock material a thin layer is poured into Petrie dishes 
from time to time, and these are used to isolate the fungus. 
The Petrie dish containing the impure mycelium is now placed on 
