1120 
is usually combined with thermal climatic stimuli, such 
as cold, wind, water, and snow. Good and bad physi- 
ological effects thus depend frequently on the totality 
of all climatic stimuli. 
METEOROTROPISM 
The preceding sections present information on the 
current status of physical bioclimatology: measurable 
weather factors produce measurable changes im man 
by biologically understandable mechanisms [16]. Such 
clear, causal relationships are rarely encountered in 
bioclimatology except in the fields of thermal and 
photochemical effects. Not even the effects of changes 
in the chemical composition of atmospheric air (COs, 
O03, N2O, I) fall into this category. 
The deleterious effects of harmful industrial effluents 
are felt by the population only if the wind has the 
proper direction, or during prolonged stable air strati- 
fication, especially in winter. All our knowledge of 
micrometeorology and austausch has to be applied to 
check this disgraceful aspect of modern artificial 
climate. Hay fever is connected with the blossoming 
time of certain species of grass, as well as with dryness 
and wind direction. All of these phenomena can, to a 
certain degree, be reproduced in the climatic chamber; 
however, in the case of head colds, headaches, and as- 
sociated diseases of doubtful origin, this is no longer 
entirely true. In considering daily and seasonal rhythms 
(except for those caused by radiation and dietary con- 
ditions) and the numerous ‘‘trigger” diseases initiated 
in the sympathetic nervous system, we have entirely 
left the field of physical bioclimatology for the field of 
“statistical bioclimatology.” 
The Effect of Periodic Weather Processes. Nearly 
every biological component from the rectal temper- 
ature to the mental disposition has a daily and a 
seasonal rhythm. Correlation of these biological ele- 
ments with any meteorological factor proves nothing 
a priori, except that weather and human life take place 
on the rotating earth. Changes im personal climate 
caused by night work or work in a mine apparently 
fail to cause an immediate change in the phase of. 
biological curves; on the other hand, in case of sudden 
change of longitude (such as by air travel) the biological 
phase seems to adapt itself within a few days (H. 
Strughold). 
The nature of the seasonal rhythm can be illustrated 
by two diseases whose causes have been recognized. 
The high infant mortality rate during summertime, 
which was formerly observed in all temperate climates, 
was due to overheating as a result of an excess of 
blankets and clothing [31] and to a lack of cleanliness 
causing an increase of the number of all kinds of micro- 
organisms. Many of these microorganisms find optimal 
living conditions during summer weather. Lack of ul- 
traviolet-produced vitamin D, accompanied by dietary 
deficiencies, leads to a wintertime peak of rickets. If 
exposure to the sun from February to April (central 
Europe) causes excessively rapid healing, that is, cal- 
cification of the bones, the calcium level in the blood 
BIOLOGICAL AND CHEMICAL METEOROLOGY 
decreases, possibly resulting in tetany of infants [31, 
61, 69]. 
Many infectious diseases show yearly variations that 
are due either to changes in the daily contact among 
people or to alterations in living conditions of micro- 
organisms. Circulatory diseases are more frequent dur- 
ing the season of greatest stress owing to sudden weather 
changes. Certain skin diseases have their peak during 
the month of maximum perspiration. The sex ratio of 
births and the pH of blood vary with the season [67]. 
The number of deaths from heart failure, suicide, blood 
pH, and the ratio of births to deaths reveal a weekly 
as well as a lunar period, according to Petersen [67]. 
The Effect of Aperiodic Weather Processes. Many 
nonepidemic diseases begin abruptly, that is, with a 
well-defined onset. Some of them have a tendency to 
begin suddenly in number, that is, the distribution of 
initial manifestations over all days of the year is by no 
means statistically random. A trigger cause must there- 
fore be present, and this has long been sought in the 
weather. The numerous attempts to hold individual 
weather elements (p, e, v, Ja, or their time derivatives, 
or oxygen content of the air, precipitation) responsible 
must be considered as having failed. Even in the case 
of head colds which may perhaps be caused partly by 
thermal effects, it has not been possible to find a 
correlation with the daily temperature fluctuations, 
except perhaps for a decrease in frequency for very 
slight temperature fluctuations and for strong winds 
[36]. Extremely low temperatures have usually failed 
to produce colds in heroic self-experimentation or in 
the case of entire armies [59]; however, a sudden onset 
of thawing weather or rain may be comcident with an 
onset of colds. On the other hand, it has been made 
possible by the methods of Linke [55] and de Rudder 
[31] to find a correlation between the incidence of 
diseases and weather fronts, prefrontal subsidence, and 
orographie foehn. 
The meteorotropic diseases have in common the 
prerequisite of a constitutional or acquired predisposi- 
tion of the individual. The predisposition may be a 
latent infection or a permanent defect such as a scar. 
They may also be partly initiated by the sympathetic 
nervous system. The weather frequently served only as 
a trigger which numerous other stimuli could provide 
equally well. Some of these diseases are ‘“‘pains due to 
the weather,” laryngeal croup, thrombosis and em- 
bolism, acute glaucoma, hemoptysis, the onset of 
diphtheria, herpes, stroke, and attacks of asthma [9, 
31]. Variations in the healthy body caused by weather 
(blood pressure, flushing of the skin, and a drop of the 
leucocyte count upon administration of NaCl) have 
also been observed. Experiments [32] have revealed 
correlations of psychological conditions with weather 
fluctuations as well as with solar activity. 
However, it must be noted that not every front acts 
as a trigger and that, in addition to fronts, other factors 
may act in the same way. Sometimes cold and warm 
fronts and occlusions act alike; sometimes their con- 
sequences are diametrically opposed. For many diseases 
