506 Mr. G. Dean. On the Nature of the [July 8, 
Summary of Conclusions, 
1. The Spiridlum Theileri is naturally transmitted by the progeny of 
Rhipicephalus decoloratus which have developed on cattle suffering from or 
recovered from Spirillum infection. 
2. It is possible to produce spirillosis-susceptible cattle and sheep by the 
injection of blood from sick or immune animals. The proof that the blood of 
immune sheep is infective is yet wanting. 
3. The pathogenic effect of Spirillum is a slight anzemia accompanied by 
fever. In none of my cases did a fatal result occur. 
An Experimental Enquiry into the Nature of the Substance im 
Serum which influences Phagocytosis. 
By GrorcE Dean, M.A., C.M., M.B., Bacteriologist-in-Charge of the Serum 
Department of the Lister Institute of Preventive Medicine, London. 
(Communicated by Professor J. Rose Bradford, F.R.S. Received July 8, 1905.) 
Metchnikoff, and his school, in the face of much opposition, lasting many 
years, have offered convincing proofs of the importance of phagocytosis in the 
protection of the animal body against bacterial invasion. The main theses of 
the Metchnikovian theory are now almost universally accepted, but the 
exact mechanism of the processes involved is even now the subject of keen 
controversy. If a highly virulent organism is injected into a susceptible 
animal, the leucocytes appear to be repelled, and to be unable to deal with 
the microbe, which multiplies and causes the death of the animal. If, 
however, the suitable immune serum is injected into the animal before 
inoculation, the phagocytes attack and devour the invading micro-organisms. 
Much discussion has centred round the interpretation of such experiments. 
The early work of Nuttall and others on the bactericidal action of normal 
serum, and Pfeiffer’s demonstration of the bacteriolysis of cholera and 
typhoid bacilli by immune sera in the absence of cells, formed the chief basis 
on which rested the humoral theory, which attributed the protection in such 
cases to the destructive action of the serum on the microbes. Fltigge 
graphically illustrated the view of the humoralists by likening the phagocytes 
to the trenches made ready behind the fighting line to receive the conquered 
dead. 
