THE PRODUCTION OF ETHYL ALCOHOL AND ACETALDEHYDE BY FRUITS IN RELATION TO THE INJURIES OCCURRING IN STORAGE: PART II. Injuries To Apples And Pears Occurring In The Presence Of Oxygén And In The Absence Of Accumulations Of Carbon Dioxide In The Storage Atmosphere

S ummary .1 Ethyl alcohol and acetaldehyde do not accumulate in apples or pears stored in air so long as the fruit remains physiologically healthy— a term which is discussed in the text. 2 (a) Apples stored in air are liable, especially at low temperatures, which are, however, higher than 0°C., to suffer from “low temperature internal breakdown” and from “soft or deep scald.” After the incidence of these diseases and as they become more profound, ethyl alcohol and acetaldehyde progressively accumulate in the unhealthy tissues. There is no evidence that the formation of these substances precedes the incidence of the disease. (b) The view is put forward that for some biophysical or biochemical reason, not as yet known, cells become unhealthy and zymasis follows subsequently as a secondary phenomenon. Supporting this view is the fact that healthy apples at an early stage in their storage experience undergo zymasis after suffering artificial injury by freezing or bruising. It is suggested that after many types of tissue injury zymasis may follow. This chain of reasoning subordinates zymasis in air‐stored apples to a pre‐existing state of incipient disorganisation which may be brought about in many different ways. (c) Diseases described in this paper are, therefore, of quite a different class from those described in Part I of this series, and chemical analysis will frequently distinguish internal breakdown and soft or deep scald from invasive aldehyde and invasive alcohol poisoning. Particularly important are the differences between deep scald and the invasive poisonings and it is urged, therefore, that the term scald should only be used for invasive diseases which occur, independently of carbon dioxide accumulation, in air stores above 0°C. (d) It is argued that the results obtained by other workers on diseases of pears in air stores can be interpreted in the same way, as in 1 and 2 (a) and (b) above, although here zymasic accumulations may aggravate the progressing disease. 3 Two interpretations of the cause of zymasis are considered: (a) Following the incidence of a state of ill health, exosmosis of cell sap occurs. Intercellular spaces become injected with liquid which hinders gaseous exchange. In the cells in those localities that consequently become poor in oxygen or very rich in carbon dioxide, zymasis occurs as a secondary phenomenon. (b) Recent gas analyses of the internal gas atmosphere of diseased pears suggest that (a) is not a universal interpretation. It is therefore suggested that, during disorganisation of the cells of pears and apples, the intricate co‐ordination of enzymes in the respiratory centres of the protoplasm breaks down; then, so long as the zymase component remains active, carbohydrate cleavage proceeds in part, at least, all the way to ethyl alcohol and acetaldehyde. 4 The disease known as superficial scald is not necessarily preceded by zymasis in the whole apple which is suffering from it.