Abstract
The authors, starting from the concept of the "normal length" of virus particles point out the dependency sometimes observed of the length of virus particles on lhe method of preparation, to which the virus sample had been submitted. ln preparations, obtained by the relatively mild methods of "dipping" or "exudation", higher percentagens of large particles can be seen, when observed with the electron microscope than in preparations of samples deriving from the same vírus source, but involving greater mechanical stress (ultra-centrifugation, alcali desintegration, ultrason-waves etc.). Generally, in preparations of this second type, the group of additional small particles (not represented in preparations obtained by milder methods) consists of rods of approxímately the same size, what agrees with the idea, that thc smaller elements are fragmente of the larg.rr particles. The rather uniform size of such fragments suggests the occurrence, in large particles, of "weak points", where a breakage under stress would easily occur. Such observations are considered .indirect proofs for the occurrence of "preferential breaking points" of virus particles. The electronmicrographies of particles of several types of vírus supply also direct evidence for the occurrence of such preferential breaking points. Sornetimes in such micrographies the particles are seen during the very process of breaking, exhibiting intact one síde of the particles borde r line and a gap on the opposite side. Based upon references of the literature and on their own observations regarding
the tobacco rattle virus, the authors point out that the supposed position of the "preferential breaking poíntsvís often acentric, what results in the fragmentation of the particle in pieces corresponding f. i. to 1/3 and 2/3 of the original size of the particle. Attention ís called upon the occurrence of biochemically weak points on the vírus particle, a phenomenon, whích does not explain but markes easier understan-dable the occurrence of comparable weak points in relation to mechanical stress.
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