Lecture XIII. 103 



nitrate. On the other hand, the higher animals at least require a 

 supply of the more complicated nitrogenous compounds such as 

 some of the higher proteins. This would indicate that plants 

 alone can build up the nuclei of these substances and that the 

 rest of living nature is in this matter, as well as in carbohydrate 

 formation, dependent on them. 



Under normal conditions Penicillium respires free oxygen and 

 of course gives off carbon dioxide and water. Its respiration is 

 aerobic. It is found that the ratio of the volume of carbon 

 dioxide given off to the volume of oxygen absorbed (respiratory 

 ratio, CO 2 : O) is dependent on the source of carbon supplied to 

 the mould ; thus with sugar the ratio is i, with tartaric acid it is 2-9. 



When Penicillium is cut off from a supply of free oxygen it is 

 found to be able to subsist by anaerobic respiration. As with 

 yeast, during this process carbon dioxide is evolved and alcohol 

 is produced. It has already been pointed out that anaerobic 

 respiration is incomplete combustion. Consequently it does not 

 render available to the plant the maximum amount of energy con- 

 tained in the carbohydrates at its disposal. When the conidia 

 germinate under conditions where anaerobic respiration only is 

 possible they bud in a manner closely resembling yeast cells. 



PRACTICAL WORK. 



From a growth of Penicillium on moist bread isolate a portion with a 

 needle, mount it in a drop of spirit, add a drop of water and cover. It is 

 necessary first to moisten with spirit because water alone will not wet the 

 conidia, which behave as if they were greasy. 



Put drops of peptone-broth-gelatine on three or four sterilised microscopic 

 slides. V\ hen it is set stab each with a sterilised needle which has touched 

 the conidia of a pure culture derived from the growth on the bread. Put the 

 slides aside in petri-dishes moistened on the inside and examine on successive 

 days. For examination it is well first to moisten with a drop of spirit, then 

 with water and cover. The preparation should then be gently warmed to 

 allow the cover-glass to settle into position. 



Careful drawings should be made of the germinating conidia and of the 

 hyphae to which they give rise, showing the coenocytic segments and the mode 

 of branching. 



When the conidiophores are mature a preparation should be exposed to 

 iodine vapour. Note the collapse of the stalk when the protoplasm of the 

 crenocytes has thus been made permeable. Main the specimen m dilute 

 Delafield's haematoxylin for 24 hours and mount and examine. Careful 

 draw ngs should be made and estimates of size recorded on the drawings by 

 means of the Ghost-micrometer. 



