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On ^Ae Relations o/Penicillilm, Torula, and Bacterium. 

 By Professor Huxley. 



{Special Seport of an Address delivered in the Biological Section of the British 

 Association for the Advancement of Science, Sept. 13th, 1870.) 



The names Penicillium, Toriila, and Bacterium are applied 

 to exceedingly humble things. That which the scientific 

 man terms Penicillium is popularly known as mould ; Torula 

 is the name given to yeast ; whilst Bacterium is so minute 

 that it has not attracted common attention, and hence has 

 received no popular name. I propose to give a statement of 

 what I imagine to be the relation of these three forms, from 

 work which I have myself lately been carrying on ; and I 

 shall have to tell you of some very remarkable facts connected 

 with their growth and development. 



It is a fact familiar to every one here that mould makes its 

 appearance on decaying matters. If you examine such a 

 growth of mould, and take some of the finer powder-like 

 matter from its surface, and placing this on a glass slide, 

 apply a high power of the microscope, you observe that the 

 grey powder which you have got on your slide consists of a 

 vast number of small spheres, of various sizes, the biggest as 

 large as the red corpuscles which are floating in my blood — 



TTTrth of an inch 



some a great deal less, not more than the 

 in diameter, the average diameter being about y-^Voth of an 

 inch. Such a body is known as a spore or conidium. On 

 applying pressure to the covering glass which you have 

 placed on the slide, you may burst some of these spores, and 

 you will find that each consists of a transparent coat or bag 

 (fig. 1), which appears to be composed of cellulose. In the 



interior of this coat is a delicate soft material, containing 

 nitrogen in addition to carbon, hydrogen, and oxygen, which 



