BOTANY 



means of an extremely fine glass needle carefully 

 manipulated have been developed in recent years, 

 and have led to results of the greatest interest. The 

 work of Kite and Chambers, in particular, in the 

 study of the physical properties of living proto- 

 plasm, nuclei, and chromosomes under these con- 

 ditions has opened up a new field of research which 

 promises to be of great value in conjunction with 

 the usual methods. 



Another new use of the microscope, in a field 

 where the biologist meets the chemist, is in con- 

 nection with colloid chemistry. By the use of the 

 so-called ultra-microscope, the principle of which is 

 the illumination of particles by a beam of light on a 

 dark background, the nature of the various types of 

 colloidal aggregation which lie at the base of proto- 

 plasmic structure and activity may be determined. 



While on this theme I cannot refrain from 

 mentioning the discovery in recent years of the 

 existence of ultramicroscopic organisms, so minute 

 as to be beyond the reach of our highest-powered 

 microscopes, and whose presence can only be de- 

 tected by the effects they produce. They pass 

 through fine-grained filters which will stop bacteria, 

 and the resulting virus can be shown to have 

 multiplied by the effect it produces. One of the 

 best known of the diseases produced by this type 

 of organism is the foot-and-mouth disease in cattle. 

 Poliomyelitis Sftd infantile paralysis, as well as other 



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