322 Brown.—Studies in the Physiology of Parasitism. 1 . 
the material obtainable by using the former liquid is in some way related 
to this marked development of attachment organs. 
In practice the removal of the film from the plate is most readily 
effected by means of a glass slide. The spore material is now thrown on 
to a muslin cloth, the edges of which are wired to a tripod in such a way as 
to form a bag, and the whole mass is subjected to vigorous washing, with 
stirring, under the tap. Any ungerminated spores, minor debris as well as 
the nutrient medium, are by this means washed away, while the weft-like 
nature of the mass of germinated spores prevents their passing through. 
This washing is continued for ten to fifteen minutes, and is followed by three 
successive washings in a large quantity (half a litre) of distilled water. The 
spore material is now strained as far as possible, spread evenly over a glass 
plate, and dried over calcium chloride in vacuo. The fungus material 
when dry is scraped off and ground in a mortar with clean, dry quartz sand. 
Throughout this work equal weights of fungus and sand have been used. 
If perfectly dry—i. e. immediately after removal from the desiccator after 
overnight exposure to the calcium chloride—the fungal skin is brittle and 
lends itself quite readily to grinding. When kept for some time in the 
ordinary laboratory atmosphere, being hygroscopic, it gains slightly in 
weight and in this state is tough and difficult to reduce to powder. In 
practice an attempt was made to make the grinding of successive lots as far 
as possible uniform in degree, this being done by the use of a system in 
grinding. The ground powder is a uniform grey, and the degree of grinding 
can be estimated roughly by the change in colour from the black of the 
unground to the light grey of the well-ground spores. Grinding has 
throughout been performed by hand, though some sort of mechanical 
apparatus could no doubt be readily fitted up. In all cases the amount of 
grinding has not been stinted, and examinations of a little of the wetted 
powder which have been made from time to time under the microscope 
have shown that only occasional spores escape destruction ; recognizable 
traces of hypha are also rare. 
As the materials of different days’ growth vary to a slight extent in 
the activity of the extract to which they gave rise, the practice has been to 
collect a considerable quantity of material, which is then intimately mixed 
up before being used for experimental purposes. This method is justifiable 
on the ground that, as far as can be seen, the dry powder preserves its 
activity undiminished for a very considerable time. Thus in one instance 
a certain tube of material appeared to possess undiminished activity after 
a two months’ interval. 1 
1 This is in accordance with the behaviour of other similar substances in the dry form. In the 
present case an exact proof is impossible on account of the difficulty of obtaining identical substrata 
at different times. The above conclusion is based upon the general effectiveness of the material 
upon a variety of substrata. 
