40 MEDICAL MYCOLOGY 



Chemotropism. — The strongest chemotropic reaction of liyphae is usually 

 negative ; the hyphae grow away from regions which have been staled by the 

 products of their own metabolism (Clark 1902, Fulton 1906, Balls 1908, Graves 

 1916, Brown 1922, 1923, 1925, Pratt 1924). A simple example of this reaction 

 is found in the circular growth of mycelia. In so far as a clear field is avail- 

 able, the hyphae tend to grow equally in all directions from the point of in- 

 fection. The same factor may account for the alternate dense and sparse 

 zones which characterize many fungal colonies. 



Energetic growth results in the deposition of catabolic substances, and 

 growth is accordingly reduced until a few hyphae pass beyond the inhibiting 

 zone and give rise to a new ring", or frequently the germination of fresh spores 

 outside this zone produces a similar effect. Ammonia and potassium bicar- 

 bonate are often among the substances producing staling, as this phenomenon 

 is called. Incubation at higher temperatures hastens staling. 



Hydrotropism may occur but is difficult to prove. 



Phototropism. — Many reproductive structures are very sensitive to light 

 and by means of this reaction adjust themselves in a position favorable to the 

 distribution of their spores, since the direction of light is usually that of the 

 direction of open spaces (BuUer 1909-1931, Jolivette 1914, Parr 1918, and 

 Blaauw 1914). It is probable, however, that there is little positive phototropism 

 among the human pathogens. 



Radium. — Little work has been done on the effect of radium on patho- 

 genic fungi. Sartory & Meyer (1926) report that in Aspergillus fumigatus on 

 media containing salt, exposure to 3-7.2 millicuries, either discontinuous or 

 continuous, produced an increase of conidiophores, with a tendency to de- 

 crease the size of the head and approach conditions found in Penicillium. On 

 media nearly free from salts, there was a tendency to form large-celled oidia 

 rich in oils, or large, thick-walled spores, 3-8/a in diameter, singly or in pairs, 

 and large pseudosporangia, 30/i, in diameter, with echinulate walls but no spores 

 observed within them. It was noted at the same time that in dissociated media 

 reducing power was lowered and pH was increased. (Sucrose 5 gm., gelatin 

 7.5 gm., NaCl 1 gm., carrot juice q. s. for 100 c.c.) In undissociated media, 

 reducing power was increased and pH was decreased. 



"With higher dosage (10.2 millicuries per sq. cm.), hard, fusiform sclerotia 

 were produced in submersed mycelium. These contained perithecia. 



BIBLIOGRAPHY 



Armstrong, G. M. 1921. Sulphur nutrition; the use of thiosulfate as influenced by hydrogen 



ion concentration, Ann. Missouri Bot. Gard. 8: 237-281. 

 Balls, W. Lawrence. 1908. Temperature and growth, Ann. Bot. 22: 557-591, 11 figs. 

 Blaauw, A. H. 1914. Licht und Wachstum I, Zeitschr. Bot. 6: 611-703. 

 Blackman, F. P. 1906. Optima and limiting factors, Ann. Bot. 19: 281-295, ^ fiffs. 

 Bokorny, Th. 1917. Benzolverbindungen als Nahrsubstanzen, Zentralbl. Physiol. 32: 55-63. 

 Bovie, William T. 1915. A direct reading potentiometer for measuring and recording both 



the actual and the total reactions of solutions, Jour. Med. Bes. 33: 295-322, 14 figs. 



