294 THE SCIENTIFIC MONTHLY
being naked or unprotected : this primitive structure is also seen in C, another type of nitrogen fixer of the soil, which is chemically more com- plex because it can obtain its nitrogen either from the inorganic nitro- gen compounds or from the organic nitrogen compounds (amino acids, proteins) which are fatal to the Nitroso monas and the Nitrobacter forms. The arrow points to a group of rods similar in appearance to those in B, A higher stage of granular structure api>ears in D, a nitrogen-fixer from the root nodules of legumes, which like B and C lives on inorganic chemical compounds but draws upon the atmosphere for nitrogen and upon sugar for its carbon: we obseFve an uneven granular structure in this cell. This may be an illustration of an early type of parasitic adaptation. The next type of bacterium (J^) is a denitrifier, which derives its oxygen from the nitrates, reducing them to nitrites and free nitrogen and ammonia. A further stage of struc- tural and chemical evolution is seen {F) in four elongated bacteria, each showing a rod-like but cellular form with a deeply staining chro- matin or nuclear mass: the arrows point to cells showing these chro- matin granules. This organism is chemically more complex in that it can secrete a powerful tryj)tic-like enzyme which enables it to utilize complex polypeptids and proteins (casein). Also it is an obligatory aerobic ty])e, being unable to function in the absence of free oxygen.
It seems that the early course of evolution was in the line of devel- oping a variety of complex molecules for performing a number of meta- bolic functions, and that the visible cell differentiation came later.^^ Step by step the chemical evolution and addition of increasingly com- plex actions, reactions, and interactions ap})ears to correspond broadly with the structural evolution of the bacterial organism in its approach to the condition of a typical cell with its cell wall, protoplasm and chromatin nucleus. To sum up, the existing bacteria exhibit a series of primordial ])hases in the capture, storage and utilization of energ}', and in the development of products useful to themselves and to other organisms and of by-products which cause interactions in other organ- isms. With the simplest bacteria which live directly on the lifeless world we find that most of the fundamental chemical energies of the living world are already established, namely, {a) the protein and car])()n storage, the primary food supply of the
living world ; {h) the colloidal cell interior, with all the adaptations of colloidal
sus])ensions, including (c) the stimulating electric action and reaction of the metallic ^n the
non-metallic elements ; for example, tlie accelerations by ^^^'
manganese, and other metals. Some bacteria carry positive,
others negative ion charges ;
11 1. J. Kligler.
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