It is superfluous to emphasize the interest with which viruses are being studied from all points of view. Their role in carcinogenesis has placed them in the limelight of cancer research, and any contribution concerning their constitution or activity is of great interest. A much debated initial problem concerns the nature of viruses and their place among the other entities. (293)

Two fundamental groups of constituents—DNA and proteins—(301, 289) have been recognized to take part in the formation of the viruses. These two groups could be separated and reunited, reproducing the original virus with all its characters. Futhermore, new viruses could be created when fractions resulting from different viruses were bound together. (289) However, the fact that a part of the virus, the DNA fraction, was seen to be furnished by the constituents of the host cell, and the protein directly by it (312), has raised the question of the nature of the virus itself. Some workers have gone so far as to see the viruses as parts of the constituents of the cells. By considering the viruses in the concept of the hierarchic organization presented above, a new aspect emerges.

According to this organizational concept, a virus represents an entity that has reached a certain step in the hierarchic evolution, and remained there throughout its individualization. Like all entities, a virus can be conceived to be formed by a principal part bound to a secondary part, the ensuing entity limited by a boundary formation. The principal part would be formed by a group of immediately inferior entities in the hierarchic scale. In the case of viruses, such inferior entities would be formed by what we could call "proviruses," which correspond to characteristic DNA formations. The principal part of the virus would be formed by the grouping together of provirus entities, proper to each virus. The secondary part is conceived to result from the immediate environment of these entities, taken directly from the host's own protoplasmatic or nuclear formation in which the principal parts are present as free entities. This secondary part is represented by the protein fraction furnished as such by the invaded nucleus or cell protoplasmatic formations. This protein fraction conserving its characteristics can be recognized and identified.

Having nuclear formations, nuclei and protoplasmatic formations as their environment, the principal part of the virus, the proviruses, multiply as proper hierarchic entities. These proviruses will leave the host usually when the cell bursts, bound this time to the proper secondary parts directly furnished by the host entity. Under these conditions, the principal part multiplied in the protoplasmatic formations or in the nucleus and the secondary parts, furnished as such by the host, would form an immediately higher entity, the virus. In the multiplication of the virus (299), the pattern followed is the same as that of other hierarchic entities. This has to occur in the proper environment which, for the viruses, is the immediately higher hierarchic entity, the nuclear level. This is represented in microbes by the individual itself, and in cells by the nucleus or by the protoplasmatic formations, which we consider to belong to the nuclear level, due to their ribonucleo proteins. It is in these nuclei or protoplasmatic formations that the viruses multiply. This explains the development of viruses in cells in compact groups, which would correspond to parasitated protoplasmatic formations and not in a diffuse form in the cytoplasma. The virus loses its secondary part upon entering the entity where it will multiply, but will take it back when it leaves its host, becoming again the entity, virus. The parasitated entity has contributed two parts to the multiplication of the virus—one, indirectly, by furnishing material which will be utilized by the provirus and transformed into its specific DNA, and two, the secondary part, directly formed by its own proteins. Like all the secondary parts, that of the virus directly furnished by the host will surround the group of proviruses forming the principal part.