September 3, 1915] 



SCIENCE 



289 



In rapidly growing tissue, such exposure 

 will cause a decrease in the rate of division 

 as well as interfering with its regularity. 

 On the other hand, an exposure of short 

 duration and of slight intensity will in 

 some cases stimulate growth, and accelerate 

 regeneration, and may perhaps cause an 

 increase in the rate of cell division. 



The literature^ on radioactivity and its 

 biological effects is voluminous, but there 

 are only a small number of papers dealing 

 with the question from a biological point of 

 view. There were a very few early papers 

 on the effect on growth and cell division; 

 they, however, were pioneers in this field 

 and their results are not far reaching. Most 

 of the work done at that time, and indeed 

 the majority of all work on the problem, 

 has sought to use radioactivity for the study 

 and solution of questions which were purely 

 medical. Of the early experiments those of 

 Perthes,* of Sehwarz^ and of Schaper'' have 

 perhaps had the most bearing on the later 

 development of the problem. These early 

 investigations were done about 1903-05. 



3 No attempt is here made to offer a compre- 

 hensive bibliography on this subject, for such lists 

 are available in Gager, C. Stuart, ' ' Effects of the 

 Bays of Radium on Plants" {Mem. N. T. Bot. 

 Garden, IV., 1908); in Warthin, A. S., "An Ex- 

 perimental Study of the Effects of Rontgen Rays 

 on the Blood-forming Organs with Special Refer- 

 ence to the Treatment of Leukaemia" (Interna- 

 tional Clinics, Vol. 47, 1906) ; in the publications 

 of Bardeen, of the Hertwigs and others. Only 

 references are here included which bear directly on 

 our present theories for the interpretation of the 

 observed effects. 



* Perthes, G., ' ' Versuche ueber den Einfluss der 

 Rontgen- und Radiumstrahleu auf Zellteilung, ' ' 

 Deutsche Med. Wochenschr. Jahrg., Bd. 30, 1904. 



5 Schwarz, 6., ' ' Ueber die Wirkung den Radium- 

 strahlen; eine physiologische chemische Studie am 

 Huhnerei," ArcJi. f. Physiol., Bd. 100, 1903. 



6 Schaper, A., ' ' Experimentelle Untersuchung 

 ueber den Einfluss der Radiumstrahlen auf Em- 

 bryonale und regenerative Vorgange, ' ' Anat. Am., 

 Bd. 25, 1904. 



The pioneer stage of the investigations may 

 be considered to end with Gager, who 

 has been the most important botanist to 

 make contributions to this subject. In his 

 monograph he sums up all of the work that 

 has been done and adds many facts from his 

 own experiments. The work of all these 

 men is representative, and may be regarded 

 as showing the state of progress at that time. 

 The results of each made a distinct con- 

 tribution to our knowledge of the effects of 

 radioactivity, and are here considered in 

 their chronological order because of their 

 bearing on the subsequent development of 

 the subject. 



The work of Schwarz is of importance be- 

 cause from his experiments he erected a 

 hypothesis, the lecithin hypothesis, to ex- 

 plain the destructive effects of radioactivity. 

 His hypothesis "was based on the fact that 

 egg yolk is decomposed by exposure to the 

 radium radiations. Although the matter 

 was not chemically determined, it seemed 

 probable that the lecithin was broken up 

 into cholin and tri-methylamine and other 

 end products of lecithin decomposition. 

 Lecithin has been found by many investi- 

 gators in all cells, especially in egg yolk, 

 spermatozoa, pollen cells, plant spores, 

 growing buds, and in all rapidly growing 

 tissue. If, then, it is destroyed, such cells 

 must necessarily be unfavorably affected" 

 (Packard). According to Schwarz the 

 effect of radiation on chromosomes and 

 other cell organs is an indirect one where it 

 occurs at all, being brought about as a sec- 

 ondary result of the decomposition set up. 

 It is especially at this point that the lecithin 

 hypothesis comes into conflict with that of 

 Hertwig, to be discussed later. 



Perthes' observations were among the 

 first from a biological point of view. He 

 exposed Ascaris eggs to radium and noted 

 that the cell divisions became slower than in 

 the controls, where no exposure had been 



