Abstract
Experiments were carried out with Escherichia coli (Strain B) bacteriophage, T2 and involved multiple infection of the bacterial host.
The infected bacilli were treated after 5 minute-, 10 minute-, or 18 minute infection, respectively. Sectioning technique of bacteria deviced by myself (at the Dept. of Infectious Diseases, School of Medicine, University of California in 1950) will be outlined as follows:
At well-defined times during the latent period, the infected bacterial cells were fixed in 0.5% osmic acid for 10 minutes. After washing and dehydration through alcohol series, bacterial pellets were embedded in methacrylate monomer, and one-tenth micron sections were cut with the Minot Ultramicrotome. Electron microscopy of sections of the infected bacteria was done with the J. E. M. type III electron microscope.
The results obtained may be summerized as follows:
a. Phage particles could not be observed in any section of the bacteria of 5 minute infection, while protoplasm often appeared in swelling in 2 or 3 parts as those shown in Fig. 1. (See page 13.) and it was noticeable that the bacilli occasionally showed a forky developing form.
b. After about half of the latent period (10 minute infection), characteristic, rather dense intracellular particles or areas were observed which seem likely to mature to morphologically perfect phage particles by the time of phage lysis. (See Fig. 2, page 13.)
c. In a sample of 18 minute infection, a large number of newly formed (replicated) T2 phage could be clearly seen in sectioned cells. The size of every phage measured 60×80 mili-micron, i.e., the same size as mature phage. Definitely it had a limiting membrane completely corresponding to mature phages. (See Fig. 3, page 14.)
Some of the cells of 18 minute infection became considerably fragile and entangled delicate fibers present in the protoplasm could be seen.
In 1951 I have tried phage studies of the same line as the present work under Dr. M. Delbrück's guidance at the California Institute of Technology.
