676 THE PARASITIC MOULDS 



and examine it to see that it does not contain more than one spore ; if there should 

 be more than one blot up some of the water with sterile filter paper until the drop 

 which remains contains only a single spore. Now place a drop of nutrient medium 

 on the -preparation and by arranging a moist chamber the growth of the fungus can 

 be studied under the microscope. 



4. Microscopical examination of cultures. In making microscopical pre- 

 parations of cultures certain precautions must be taken. The simplest method 

 is to cut off a small piece of the mould with a pair of fine scissors and transfer 

 it to a drop of alcohol on a slide water must not be used because not only 

 does it fail to wet the fungus properly but it also causes the sporangium to 

 burst cover with a cover-glass and run in a drop of glycerin. This is easily 

 done by placing a drop of glycerin at one edge of the cover-glass and drawing 

 it through with a fragment of blotting paper held at the opposite edge. 

 Another method is to place the mould in a drop of 0*5 per cent, osmic acid 

 on a slide, leave for a few minutes, wash in alcohol then in distilled water 

 and finally mount in glycerin. The preparation may, if necessary, be stained 

 in an aqueous solution of safranin after soaking in osmic acid. 



The following is the method recommended by Salomonsen when it is desired 

 to examine a whole colony. Transfer a young colony to a slide, cover gently 

 with a cover-glass, allow it to dry for a few minutes and then place a large 

 drop of osmic acid solution at one edge of the cover-glass. When, after a 

 few minutes, the osmic acid has thoroughly penetrated the preparation, blot 

 up the excess and run first a drop of water and then a drop of glycerin 

 under the cover-glass. 



5. Inoculation experiments. Attention was first drawn to the pathogenic 

 properties of some of the Mucors (the white moulds) by Lichtheim and by 

 Lindt and the observations of these investigators have been confirmed by 

 Lucet and Costantin. 



The severity of the disease following inoculation of these fungi depends 

 not so much upon the virulence of the parasite as upon the number of indi- 

 viduals inoculated ; and herein they present a great contrast to the bacteria. 

 This may be explained by the fact that though the spores germinate when 

 introduced into the tissues, reproduction has never been known to occur in 

 the body. Direct transmission of the parasite from animal to animal has 

 never been observed ; when infection occurs, it is the result of the inocula- 

 tion of spores. It is not possible to produce an infection by direct inoculation 

 of portions of the mycelium, and before infection of an healthy animal can 

 be effected spores must have been formed outside the tissues of the living 

 body. 



A disease fatal in a few days follows the inoculation of the spores of Lich- 

 theimia corymbifera, Mucor pusillus, etc. into the veins or peritoneal cavities 

 of rabbits ; and when the tissues are examined post mortem numerous mycelial 

 threads will be found in the kidneys (which show lesions of nephritis), Peyer's 

 patches and also in the lungs (Lichtheim, Barthelat). The inoculation of 

 Rhizomucor parasiticus into the veins of rabbits, guinea-pigs or fowls also 

 leads to a fatal disease (Lucet and Costantin). 



SECTION I. THE GENUS MUCOR. 

 Mucor mucedo. 



Mucor mucedo is one of the moulds most commonly found in food-stuffs 

 and other organic matter. It grows luxuriantly producing tall, whitish, 

 woolly-looking tufts. The mycelium is branched and gives rise to tall spore- 

 bearing hyphae or pedicels, each of which is swollen at its distal end into a 



