33^ LiacocvTo(.ki:(;AKixES. 



the dog ultimately have a thin covering arotind them, termed a 

 cytocyst, while within the host cell, and are thus separated from 

 the nucleus of the host cell. Free vermicular forms are also seen 

 in the blood plasma. The intra-corpuscular or cytozoic forms 

 average from Sfi to I2fi by 4.5/a to O/m broad. The parasite usually 

 has a well-marked nucletis. 



Multiplication of L. canis by schizogony, that is, by the 

 asexual method of multiple fission, has been observed by me in 

 the bone marrow, liver, and spleen of the dog that dipd in 

 Johannesburg. I have some evidence of asexual multiplication 

 of L. leporis in the lungs of the rabbits used by me. Schizogony 

 of L. muris occurred in the liver of the rats examined. No 

 definite sexual reproductive forms occtirred in the blood of the 

 vertebrate hosts. The parasite was apparently transmitted to the 

 dog by the tick, Rhipiccphalu^ sanguineus, and from rabbit to 

 rabbit and rat to rat by mites. 



The pathogenicity of leucocytogregarines varies. It has 

 already been mentioned that L. canis was fatal in the case of Dr. 

 Becker's dog, which died after a fortnight's illness, having shown 

 much anaemia and emaciation, rise of tenij^erature, and some 

 diarrhoea. No parasite other than L. cam's was found at autopsy. 

 Similarly, white rats infected with L. muris died at Washington, 

 U.S.A., about 1907, as reported by the late W. W. Miller, and 

 L. niusciili caused outbreaks of disease among some white mice 

 in England ab<^ut the same time, as reported by Porter. 



(Read. July 10, igi8.) 



Stbllar Catastrophes. — Prof. 11. N. Russell, of 



Princeton University Observatory, in his jjresidential address to 

 Section A (Astronomy) of the American Association for tlie 

 Adva!icement of Science, at its Baltimore meeting, drew s])ecial 

 attention to the catastrophes which happen every few years, or 

 oftener. in our galax)', and aj^parently every few weeks in the 

 Andromeda nebula — catastrophes which in magnitude transcend 

 all other known ])h}sical phenomena. Two possibilities suggest 

 themselves — a collision or an explosion. Collisions between two 

 stars are out of the ([uestion ; collisions between stars and nebulae 

 may account for most of the phenomena, but the s]>ectra observed 

 are not thus satisfactorily explicable. Collisions between stars 

 and small dark bodies are also attended with difficulties. Know- 

 ing what we now do about the stores of energy locked uj) within 

 the atom, the ])0ssibility of an explosive release of some such 

 form of energy within a star may be suggested. Prof. Russell, 

 however, inclines to favour the collision iheory as the most 

 ))romising. supported as it is by the fact of the great frequency 

 of novae in .spiral nebulae. 



