MODERN MEDICINE DO AN 517 



in the body economy. A lack of calcium may lead to hyperirritability 

 of the nemo-muscular mechanism, tetany. A deficiency in iron leads 

 to hypochromic anemia, and, if iodine is not available, the thyroid 

 gland suffers. In this connection it is important to remember that 

 interference with absorption or utilization of essential specific principles 

 may be quite as significant in producing symptoms as their absence 

 from the diet. 



Also a new principle in disease has been recognized very recently 

 through the increasing knowledge of the interdependence and interac- 

 tion of vital physiologic functions between widely separated and appar- 

 ently unrelated organs. If the function of one is impaired the normal 

 function of the other may lead to premature or untimely invalidism or 

 death. As examples, may be cited the removal of the normal thyroid 

 gland to recompensate the damaged heart — or the elimination of the 

 spleen in selected instances where it acts to inhibit or make less 

 effective the production of blood cells by the bone marrow. 



One of the most fascinating fields for speculation and further investi- 

 gation at the present moment lies with the ultramicroscopic viruses. 

 Since the original demonstration of the infectious properties of filter- 

 passing sera from which neither aerobic nor anaerobic bacteria 

 could be cultivated, the question of the ultimate nature of these agents 

 has been warmly debated. Do they represent minute living and 

 propagating protoplasmic bodies or are they more nearly comparable 

 to chemical hormones or enzymes? Within the past few months 

 Stanley, plant pathologist at the Rockefeller Institute, Princeton, has 

 reported the isolation, purification, and chemical crystallization of the 

 agent which produces mosaic disease in the tobacco plant. Thus, 

 the possibility of an entirely new set of biological phenomena related 

 to complex chemical molecules is suggested, and the differential criteria 

 separating animate and inanimate molecular structures are reduced 

 almost to the vanishing point. Many of the workers in this field at 

 the present time, while accepting the nonviable nature of tobacco 

 mosaic virus, still believe that other of the viruses may be the earliest 

 and most primitive forms of living matter. Chemistry and biology 

 must, therefore, again function together as handmaidens to pathology. 



The plant and the animal pathologist often serve as pioneers in 

 exploring territories in which diseases common also to man exist. 

 Laidlaw's investigations of distemper in dogs and his development 

 of an immune vaccine and therapeutic serum, have given fresh impetus 

 and direction to the search for an effective control of the common cold 

 in man. And Shope's study of the swine influenza which appeared in 

 1918, coincident with the world-wide spread of human influenza, 

 identified a common etiology for the two diseases through common 

 immunologic reactions. Shope found, however, that in swine it required 

 both a filterable virus and a bacterium closely similar to, if not identi- 



