420 CHARLES RUSSELL BARDEEN 



INTRODUCTION 



In a brief communication presented at the 1908 meeting of the 

 Association of American Anatomists and published in the Anatom- 

 ical Record, April, 1909. I have summarized the results of experi- 

 ments which showed that spermatozoa, ripe ova, and newly fertilized 

 ova of the frog and toad are very susceptible to the X rays, that 

 the susceptibility decreases early in the second hour after fertihza- 

 tion, then rapidly increases to a maximum during the earlier 

 cleavage stages, and finally greatly decreases during the period 

 of gastiulation. In 1909 and 1910 further experiments have 

 served to confiim these results and to throw some new light on 

 the nature of the effects of X rays on living tissues. In order 

 that the more general bearings of these experiments may be the 

 better appreciated it seems advisable, before describing the 

 experiments in detail, first brieflj^ to review work of various 

 investigators which seems to give insight into the fundamental 

 features of the action of the X rays on protoplasmic activity. 



The activities of protoplasm may be divided into three corre- 

 lated groups, sensory-motor, metabolic, and morphogenic. 



Exposure to the X rays apparently does not directly disturb 

 the sensory-motor activities. Motile unicellular organisms and 

 the spermatozoa of the higher organisms seem to move about as 

 freely when exposed to the rays as when not thus exposed. ^ 



Joseph and Prowazek have described in Paramoecia and Daph- 

 nia a negative tropism toward the Roentgen rays. This is cer- 

 tainly not well marked in the paramoecia with which I have 

 experimented. Paramoecia exposed for twelve hours to the 

 rays showed no disturbance in freedom of movement either dur- 

 ing exposure or subsequently. Muscular and ciliary activity 

 in planarians exposed to the X rays for considerable periods was 

 apparently not directly affected by this exposure. Specimens 



iBohn, Comptes rendus de I'Acad, de Sciences T. 136 1903, p. 1085 states that 

 171 vitro radium rapidly causes cessation of motion in the spermatozoa of the sea 

 urchin, llertwig, 1910, on (he contrary finds that IG to 23 iiours exposure to 

 radium does not affect the motility or the fertilizing capacity of the sperma- 

 tozoa of soa urchins. 



